The present invention relates to an electronic musical instrument which generates musical sounds by means of digital circuitry, and more particularly to an electronic musical instrument in which an envelope value is changed in asynchronism with a musical sound waveform.
As electronic technologies have rapidly progressed, it has become possible to generate sounds of musical instruments by electronic circuits. For example, an electronic piano generates the waveform of each sound of a piano by an electronic circuit, amplifies the waveform by an amplifier and emits the musical sound from a loudspeaker. Likewise, an electronic organ generates the waveform of a musical sound corresponding to a depressed key by an electronic circuit, amplifies the waveform by an amplifier and emits the musical sound from a loudspeaker.
Such electronic musical instrument generating the musical sound by electronic circuit assimilates this musical sound more to the sound to be produced from the acoustic musical instrument, by varying the envelope or the amplitude value of the sound with time. The musical sound is not emitted with its maximum value simultaneously with the depression of the key, but is produced as follows by way of example. First, an attack status is established, and the envelope value increases. When a specified value has been reached, a decay status is established, and the envelope value remains the specified value for a predetermined period of time. After the predetermined period of time, a release status is established, and the envelope value decreases slowly. The release status ends when the envelope value has become zero.
Meanwhile, the electronic musical instruments are classified into types which generates the musical sounds by analog processing, and types which generates them by digital processing.
The type based on analog processing is favorable in case of forming one sort of tone color, but its circuit arrangement becomes complicated in case of forming a plurality of kinds of tone colors. This is because the tone color of one musical instrument is produced by disposing a filter having a specified frequency characteristic. In order to emit a plurality of kinds of tone colors, a plurality of filters must be used. Further, a plurality of analog multiplier units are required for changing the envelopes independently of one another.
The type based on digital processing generates the waveform of the musical sound in terms of a digital value, and converts the digital value into an analog value by the use of a D/A (digital-to-analog) converter. A clock signal corresponding to the depressed key is generated, the pulses of the clock signal are counted by a counter, the count value is used for reading the content of a waveform memory in which waveform data are stored, and the digital data of the waveform is formed. The waveform data stored in the waveform memory are the differentiated values of the waveform, and the data read out from the waveform memory are accumulated for forming the digital data of the waveform.
The change of the envelope or amplitude in the digital processing is effected in such a way that the differentiation data of the waveform read out from the waveform memory is multiplied by the envelope value and that such results are accumulated.
While electronic musical instruments include the analog type and the digital type as stated above, most of them resort to digital processing at present because digital processing can be simply performed owing to the progress of the LSI technology.
Also the electronic musical instrument based on the digital processing performs the processing involving the attack, decay and release statuses described before. In the case of the digital processing, the accumulated result is not multiplied by the envelope value, but differentiation data of the waveform before the result is multiplied by the envelope value. In general, the envelope value is changed at the timing at which the cumulative value becomes zero.
FIGS. 1A to 1G show a timing chart depictive of the various timings of the electronic musical instrument in the foregoing case where the timing of the multiplication corresponds to the cumulative value of zero.
FIG. 1A shows the timing clock EXC of the waveform. This timing clock EXC of the waveform enters an address counter which appoints the address of a memory storing basic waveforms therein. By way of example, the address counter is a counter of 2 bits, which accesses the memory storing the differentiated values of the basic waveforms therein and causes it to deliver the corresponding differentiation data each time the timing clock EXC is inputted.
The waveforms shown in FIG. 1 will be explained below on the assumption that pulse-shaped waveforms are stored in the memory. More specifically, one waveform is composed of four clock pulses. The differentiation data of the basic waveform is "+1" at timing clock EXC1, "0" at timing clock EXC2, "-1" at timing clock EXC3, and "0" at timing clock EXC4. They are successively outputted from the memory.
FIG. 1B shows a synchronizing signal SYNC. An attack signal ATT (FIG. 1C), an envelope clock EVCK (FIG. 1D), an envelope value EV (FIG. 1E) and an envelope status EVST (FIG. 1F) change in synchronism with the synchronizing signal SYNC.
The attack signal ATT is a signal indicative of the start of the attack, and is delivered when a key is depressed. That is, the envelope status EVST becomes the attack AT in accordance with this signal. The envelope clock EVCK is a signal which affords the timing of the change of the envelope, and by which the envelope value EV is changed. The envelope value EV is 0 at the start of the attack, and becomes 3 simultaneously with the clock of the start. Therefore, the musical sound waveform MW (FIG. 1G) rises from 0 to 3 in accordance with the timing clock EXC1. The envelope value EV does not change at the timing clock EXC2, timing clock EXC3 and timing clock EXC4, and the differentiation data of the waveform is "-1" at the timing clock EXC3, so that the musical sound waveform MW changes from 3 to 0 again. At the next pulse of the synchronizing signal SYNC, the envelope value EV becomes 6, and the musical sound waveform MW becomes 6. At the still next pulse of the synchronizing signal SYNC, the envelope status EVST becomes the decay DC, and the envelope value EV becomes 7. The decay DC in FIG. 1F has a short duration, and changes into the release RL at the next clock. In the release RL, the envelope value EV changes to be 6, 5, 4, 3, 2 and 1 at the successive pulses of the synchronizing signal SYNC. Finally, the release RL ends, that is, the amplitude becomes 0.
In the case of FIGS. 1A to 1G, the envelope value EV is always changed when the value of the waveform, namely, the cumulative value becomes 0. Thus, the cumulative value finally becomes 0 without fail. Since this method changes the envelope value EV in synchronism with one cycle of the musical sound or one waveform, only one timing for changing the envelope value EV exists within one cycle. Therefore, the method cannot change the envelope value EV, e. g., from 0 to 7 slowly and greatly within one cycle, in other words, to be 0, 1, 2, . . . and 7 within one cycle, and it can afford only such great changes of the envelope as being 0, 4 and 7 in succession. In the example of FIG. 1, the envelope value is changed to be 3 and 6 in two cycles. This results in increasing the varying width of the envelope, and is equivalent to decreasing the apparent number of bits of the envelope. Accordingly, the prior art involves the problems of the occurrence of clock noise, etc., which lead to musical sounds offensive to the ears.
On the other hand, to the end of solving the problems, there has been proposed a method in which the envelope value EV is changed without being synchronized to the synchronizing signal SYNC.
FIGS. 1H to 1K show a timing chart of the system which changes the envelope in asynchronism with the synchronizing signal SYNC. The timing clock EXC, synchronizing signal SYNC and attack signal ATT in this case are the same as those in the foregoing case, and reference should be had to FIGS. 1A to 1C. In this system, an envelope clock EVCK' and an envelope value EV' change in asynchronism with the synchronizing signal SYNC. By way of example, simultaneously with the attack signal ATT, an envelope status EVST' becomes the attack AT, and the envelope value EV' becomes 1 in accordance with the envelope clock EVCK'. Since, at this time, the timing clock EXC1 is +1, a musical sound waveform MW' changes from 0 to 1. Subsequently, irrespective of the synchronizing signal SYNC, the envelope clock EVCK' is outputted, and the envelope value EV' becomes 2. Although the timing clock EXC2 exists meantime, the musical sound waveform MW' at this timing does not change because the basic waveform data is 0. The reason is that the basic waveform data of this system are differentiated values, and that the musical sound waveform MW' is obtained by multiplying the basic waveform data by the envelope value and accumulating such products. The envelope value EV' becomes 3 at the same time as the next envelope clock EVCK'. Since, however, the timing clock EXC is not outputted yet at this point of time, the musical sound waveform MW' does not change. The change is effected by the timing clock EXC3. This is because the basic waveform data is -1 at the timing clock EXC3. That is, the basic waveform data and the envelope value EV' are multiplied and the product is cumulated in response to the timing clock EXC3. As a result, the musical sound waveform MW' becomes -2. Likewise, the envelope value EV' is successively changed to be 4, 5, 6 and 7 by the envelope clock signal EVCK', and the envelope status EVST' becomes the decay DC. Thus, the musical sound waveform MW' changes from -2 to be +3, -4, +3 . . . Further, the envelope status EVST' changes from the decay DC into the release RL, and the envelope value EV' decreases to be 6, 5, 4 . . . and finally becomes 0. When the envelope status EVST' is the release RL, the duration of the envelope clock EVCK' is long, with the result that the musical sound waveform MW' decreases slowly. The above operations are repeated in succession. With this system, the musical sound waveform MW' does not become 0 in some cases in spite of the fact that the envelope value EV' has finally become 0, whereupon the release RL has become 0. The musical sound waveform MW' shown in FIG. 1K is -1 at this time.
With the system wherein the absolute value of the musical sound waveform is obtained in the final accumulation part as stated above, a DC (direct current) component is left behind when the envelope value has been changed at any other time than the time at which the cumulative value becomes 0. When the operations of depressing keys and generating musical sounds have been successively repeated, the DC component becomes large and sometimes exceeds the dynamic range of the D/A converter. Due to the presence of the DC component, the cone of the speaker does not oscillate at a predetermined position, and it recedes deep or bulges frontwards. In this manner, several problems are involved in the system which change the envelope value asynchronously.